Solid high performance AF, great high ISO performance up to 3200, the handling you would expect from a 1-series camera, and files that take PP extraordinarily well.

Cons:

Nothing I can think of at the moment.

I've been shooting the Mark IV for over a month now and I have been delighted by what I've experienced so far. As a wildlife shooter my keeper rate for Birds in Flight has increased by at least 30% over what I was getting from the Mark III and that tickles me pink!

Focus aquisition is fast, accurate and precise. The details I am seeing when used in combination with my 500 f/4 are more impressive than I ever would have imagine. I can't say that more pixels matter but I have no other explaination.